Conventionally, a small internal combustion engine such as a diesel engine or a gasoline engine has high general-purpose properties and is employed for various purposes such as an agricultural machine, a construction machine and a ship (loaded machine). Accordingly, loading space of the internal combustion engine is various corresponding to the loaded machine, and the loading space of the internal combustion engine may be small.
In an internal combustion engine having a DPF (Diesel Particulate Filter) effective for dealing with regulation of exhaust gas, the ratio of the space for the DPF to the space for the whole internal combustion engine is large.
Therefore, different specifications are set about the loading position of the DPF in the internal combustion engine so as to follow the installation position and exhaust direction of the loaded machine.
For example, as the loading position of the DPF in the internal combustion engine, the construction in which a DPF 200 is arranged above a manifold 210 as shown in FIG. 12(a) and the construction in which the DPF 200 is arranged above a flywheel 220 as shown in FIG. 12(b) are provided.
When the loading position of the DPF is changed, the shape of the exhaust manifold is also changed.
For example, in the construction in which the DPF is arranged above the exhaust manifold (FIG. 12(a)), an exhaust outlet of the exhaust manifold must be directed upward, whereby the shape of the exhaust manifold as shown in the Patent Literature 1 is employed.
In the construction in which the DPF is arranged above the flywheel (FIG. 12(b)), the exhaust outlet of the exhaust manifold must be directed to the flywheel, whereby the shape of the exhaust manifold as shown in the Patent Literature 2 is employed.
Furthermore, as a measure for reducing NOx and the like discharged from the internal combustion engine, in addition to the DPF, a method is employed in which a part of exhaust gas discharged from the internal combustion engine is returned to the intake as EGR gas (EGR: Exhaust Gas Recirculation). In this method, mixture ratio of the exhaust gas (EGR gas) and new air (EGR ratio) is changed corresponding to the positional relation between an EGR taking-out section and an exhaust gas discharge section guiding exhaust gas to a silencer in the exhaust manifold.